Homework Help:
Voltage in a 2 battery series circuit

1. The problem statement, all variables and given/known dataWhat is the magnitude and direction of the current in the following circuit?
[URL=http://imageshack.us][PLAIN]http://img234.imageshack.us/img234/7587/circuituk2.gif[/URL][/PLAIN]
resistance for series: Req=R1+R2+R3+R4....etc
Kirchhoff's rules --> Loop Rule: sum of potential drops must equal sum of potential rises
V=IR

My question is this: Why am i not supposed to add the voltages (30+10) together when solving this problem?? If i solve for this problem in the following way, 30V-10V = I(52ohms) then i get .38 Amps clockwise (which is right) but i don't understand why i have to subtract the voltages!

Yes, the equivalent voltage will either be a sum or (in this case) difference of the 2 voltages. Going in a clockwise loop from A, a particle will go from low potential to high potential (+30V) and then go from high potential to low potential (-10V). If the batteries were arranged + to - in series, you could add the voltages because there would be a rise followed by another rise

the kirchoff's rule as a whole. I tried solving this problem in the following way :
R= 1/32 + 1/20 = 0.083 ohms
I= V/R = 30/0.083= 360 amps
which I know is wrong so what can I do, I spent the last hour watching a professor from MIt working a similar problem yet he did not show it with numbers or real answers.